Transferring molybdenum from spent catalyst to fresh solid catalytic material



n l H. T. BROWN 2,367,263 TRANSFERRING MOLYBDENUM FROM SPENT CATALYST 1 Jan. 16, .1945.

TO FRESH SOLID CATALYTIC MATERIALl Filed Dec. 26, 1942v Jiri ` Patented Jan. 16, 1945 v TRANSFERRING MOLYBDENUM FROM n SPENT CATALYST T FRESH SOLID l CATALYTIC MATERIAL Henry Trueheart Brown, Whiting, Ind., assigner to Standard Oil Company, Chicago, Ill., a corporation of Indiana Application December 26, '1942, Serial No. 470,278

claims., (c1. 252-238) This invention relates to a process of recovering molybdenum and morek particularly vto a process of recovering molybdenum fromVv spent catalysts in which molybdenum forms an essential ingredient.; In the hydrogenation of coals, tars, oils and other--carbonaceous materials, in

the catalytic dehydrogenation of oils, gases, pe-

troleum hydrocarbons,r and the catalytic `dehy droaromatizationl 'of paraiiinic and naphthenic hydrocarbons, the -hydroformin'g' of naphthas, etc.; catalysts 'containing molybdenum have been -employed to a great` extent. `These vcatalysts usually combine molybdenum oxide in a minor amount with a maiorproportion ofother cataLvtic ingredients .such as' active silica, for examplekieselguhr orA silica gel,.active alumna, for

denum may be absorbed directly,` from the HCl gas onto variouscatalyst supports, e. g. activated alumina, active silica, or active charcoal, and then employed again for the treatment of carbonaceous lmaterials.l etc.

My invention isillustrated by aldrawing which lshows schematically lin 'vertical section an apparatus for recovering molybdenum from a spent catalyst. ,Referring to the drawing, the spent catalyst in powdered or granular form is introduced by hopper I0 into furnace H; Various l types of furnaces may be` employed for this'purl example alumina gel or bauxite, titanio., zinc oxide, etc.- The ,amountr of lmolybdenum or molybdenum loxide employed in the preparation of such catalysts vis usually of the order of 1 to 25percent and generally about 5 to 10 percent. Inasmuch as Vthe molybdenum V is Vthe most valuable ingredient of the catalyst', considerable yeiit'ort has been .put forthto recover it from the spent catalyst after the catalytic activity has decreasedr to a pointvwhere it is'nolonger ecopose, for example a rotary kiln may be used, or

the 'catalyst may be deposited iny a bed in an insulated chamber and heated -by superheated hydrogen chloride gas employedinthe operation. The drawingl showsa typical wedge furnace in which the catalyst is" moved by plows carried on rabble armsv across and downward over a series of hearths indirectly heated by means not shown. After passing through the furnace' II the catalyst is discarded at I2.

nomic to continue using' it. Various methods havelbeen proposed 'for this purpose, generally involvingv conversion of -the molybdenum in the catalyst into an alkali soluble form in which it is extractedfrom the spent catalyst by -various aljkaline solutions. These processes are beset with the diiliculty of obtaining the molybdenum in a form in Vwhich it is suitable for reuse in thev preparation of catalysts. -They also require expengsive extraction and washing operations.

I have -now discoveredthat molybdenum may be recovered Vfrom spent catalysts and other materials by volatilizationor sublimation in a current of hydrogen chloride gas passed :'nto the catalyst material at an elevated temperature. Under these conditions the molybdenum appears to form a volatile complex 'oxychloride By this method I have been able to recover 8 0 percent The molybdenum" recovered by myprocess isA in a highly purified form substantially free from contamination by other metals. The complex Hydrogen chloride gas is introduced by line I3 at a low point inthe furnace and passes up ward over and through the catalyst descending through the furnace,y departing by line I4. The. temperature ofthe furnace may be maintained within the range of about 400 to 1000 F., preferably vaboutliOO to 750 F. The desired temperatu're depends to a large extent on .the char. acter ofthe material treated,V the volume of HC1 employedand the time of contact .provided in the furnace.

Where powderedrcatalysts are treated itfmay be' necessary vto dedust the HCl-molybdenum 1 gases leaving rthe furnace in order toprevent' contamination of the ,molybdenum product with thehgases are cooled'and the molybdenum chlochloride may be converted into molybdic acid or ride complex separates as 'a whitel crystalline material to be removed periodically through the fbottom head I6. Receiverl5 may be equipped with suitable scraping apparatus (not shown on the drawing) to maintain relatively clean re ceiver walls and' to transfer sublimed molybdenum oxide complex to the bottom of said receiver. HC1 gas passes out at I1 and thence through line l'and blower I9 discharging vby' line 20 back to the furnace II. lIn this manner the- HC1 gas may be recycled until gaseous impurites accumulate in the system to an undesirable extent at which time the system may be purged of gas by venting through valved outlet 2l. The system is then recharged with fresh HC1 gas.

Instead of separating the molybdenum chloride complex as just described, the hot hydrogen chloride gas carrying molybdenum may be passed by line 22 to catalyst activating tower 23 in which the HC1 is contacted with a stream or moving bed of adsorbent catalytic material, for example activated aluminum oxide, introduced through hopper 24. The molybdenum is substantially completely adsorbed on the alumina and the denuded gases are conducted by line 2liA and lines i8 and 20 back to the furnace Il. The activated alumina is ypassed from tower 23 by star valve 26 Vinto hydrolyzing chamber 21 wherein steam may be introduced by line 28 in a suflicient amount to hydrolyze the molybdenum compound on the catalyst and convert it to molybdenum oxide. The chamber 21 is provided with gas vent 29 near the top. Catalyst is withdrawn from chamber 21 by outlet 30. It may be employed directly in the treatment of carbonacecus materials or it may be subjected to calcining' at elevated temperature, e. g. 800 to 1200* F., before use. Any hydrogen chloride adsorbed or occluded in the catalyst can be driven oi in the calcining operation.

As an example of my process, aluminum oxide catalyst containing about l percent molybdenum oxide was used in the hydroforming of petroleum heavy naptha in the process of converting the heavy naptha to a gasoline of high knock rating containing an increased amount of aromatic hydrocarbons. In this process, naptha vapors are passed through a bed of catalyst held at a temperatui'e of about 900 to 1000 F. in the presence of hydrogen gas supplied at a pressure of about 400 pounds per square inch. The rate of treating was maintained at about 0.5 to 2 volumes of naptha per hour per gross volume' of catalyst and hydrogenous gases recovered from the process were recycled at the rate of about 2500 cubic feet per barrel of naptha charged. Under these conditions the operation was continued forseveral hours, then the operation interrupted, and the catalyst regenerated by combustion of air at a temperature between about 900 and 1200 F. This cycle was repeated for a period of wee or months until the activity of the catalyst was permanently 'impaired to an uneconomical extent. The catalyst was then considered spent and was removed from the operation and replaced with fresh catalyst.

The spent catalyst withdrawn` after regeneration from the above operation and containing about 8 percent molybdenum was treated thirty minutes at a temperature of 700 F. with a stream ofV hydrogen clhloride gas. On cooling the gas withdrawn from the catalyst, molybdenum oxychloride complex was deposited as a white crystalline compound. In one experiment 71 percent of the molybdenum contained in the catalyst was recovered. In another experiment, under i substantially the same conditions, 'I3 percent was recovered. In another experiment, with longer treatment, approximately 80 percent of molybdenum oxide was recovered.

Another experiment conducted at 580 F. yielded molybdenum in the amount of 66.4 percent of that contained in the spent catalyst. Further roasting of the catalyst after molybdenum recovery converted the residual molybdenum into a form susceptible to some further recovery by treatment with HC1 gas.

The molybdenum is obtained from the recovery process in the form of snowy crystals extremely lysts. When a water solution of the complex is reduced by the action of zinc dust, etc. the characteristic molybdenum blue is obtained.

The reaction between the hydrogen chloride and the molybdenum in the catalyst is not clearf ly understood. It appears that only the molybdenum in the form of one particular oxide may be sublimable with HC1 which would account for the fact that only about 70 percent of the molybdenum in spent catalyst is easily recoverable. As evidence of this is the fact that the hydrocarbon conversion operation effects a change in the chemical relation of the molybdenum oxide with respect to the alumina in the catalyst which change facilitates its recovery by the action of HCl gas, but the nature 'of this chemical change is not known. Whether the garbonaceous matter forms a compound with the molybdenum in the catalytic process, or whether it is simply a matter of reduction of molybdenum trioxide to a lower oxide is not established, but the latter explanation seems improbableconsidering the frequent regeneration ofv the catalyst by burning in the process and considering that roasting and ignition of the spent catalyst in air prior to HC1 treatment does not prevent molybdenum recovery by my method. In fact, my method may be applied to the spent catalyst either before or after regeneration. The data obtained indicate that for optimum results in my process the hydrogen chloride gas should be essentially dry.

Having thus described my invention what I claim is:

`chloride gas from said adsorption operation is recycled to said vaporizing operation.

3. The process of claim 1 wherein suflicent molybdenum chloride complex is adsorbed on said active aluminum oxide to be equivalent to 5 to 10 per cent of molybdenum oxide based on the weight of the catalyst.

4. The process of transferring molybdenum from spent molybdenum-activated catalyst to fresh solid catalytic materials which comprises passing a current of HC1 gas through said spent catalyst at an elevated'temperature whereupon the molybdenum is vaporized from said spent catalyst in the form ci a complex chloride, thereafter contactlnssaid gas and molybdenum complex chloride vapors at a. lower temperature with a solid catalytic material onto which said molyb-Y denum chloride complex is adsorbed and subjectinz the solidk catalytic material containing adsorbed molybdenum chloride complex to hydrolysis to convert the molybdenum complex to molybdenum oxide thereby electing its catalytic activation before use invcatalytlc processes.

5.- The process of transferring molybdenum from spent molybdenum-activated catalyst to freshsolid catalytic materials which comprises.

passinc a current of HC1 sas through said spent catalyst at an elevated temperature whereupon 18 l '3 the molybdenum is vaporized from Ysaid spent catalyst in the form of a complex chloride, thereafter contacting said gas and molybdenum complex chloride vapors at a lower temperature with Y a solid catalytic material onto which said molyby HsNRY TRUEHEART BROWN. 

